1. Field of the Invention
This invention relates to an oscillating roller assembly in an offset printing press and, more particularly, to such an oscillating roller assembly in which the oscillating roller is driven to oscillate by means of fluidic pressure.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97-1.99
Offset printing assemblies are well known which employ one or more oscillating rollers in either or both of the dampening liquid roller train and the inking roller train. These oscillating rollers oscillate back and forth in the axial direction while in contact with an ink carrying roller, dampening liquid carrying roller or ink and dampening liquid carrying roller. When such oscillating rollers are used in the dampening liquid train, the uniformity of water film thickness on the printing plate cylinder is enhanced. In addition, use of an oscillating roller increases the speed of cleaning the printing plate during start-up and thereby reduces start-up waste. Further, scumming at the edges of the printing plates is reduced or eliminated which also reduces waste and enhances print quality.
It is known to drive such oscillating rollers via complex gear trains and cams. Due to such complexity, such gear train driven oscillating rollers cannot be used in inking rollers and dampening rollers without tremendous cost.
More recently, such oscillating rollers have been friction driven via contact with vibrating drums which are printer driven and oscillate themselves to cause the oscillating rollers to oscillate. These vibrating drum driven oscillators, or self-oscillating rollers, function successfully but they provide no means for control of the oscillation which is generally random. In addition, such self-oscillating rollers require vibrating drums to drive the oscillatory movement that entail additional complexity and cost of construction and also result in increased cost of maintenance and repairs.